New technologies implemented to reduce the consumption of motor vehicles and their pollutant emissions often require multiple circuits or loops for regulating the temperature.
By thermal regulation loop is meant a circuit in which circulates a coolant which regulates the temperature of a mechanical member by conveying the thermal energy produced by the operation of this member.
For example, on a hybrid-type vehicle, two, three or four regulation loops can be found which are each dedicated to the cooling of a particular member with has a specific requirement in terms of thermal management.
By way of example, a vehicle of this type may have:                a high temperature regulation loop for regulating the temperature of the heat engine,        a low temperature regulation loop for regulating the temperature of the power electronic members of the electric propulsion chain,        a very low temperature regulation loop for regulating the temperature of the propulsion battery.        
For reasons of compactness and cost limitation, some equipment, such as the degassing tank, may be shared with several regulation loops.
Degassing is an important function during which the air or gas bubbles that are present in the coolant are purged.
Degassing is an important function because the presence of air bubbles in the coolant has a deleterious effect on the quality of the cooling, and therefore does not allow engine operation in optimal conditions, which can lead to uncontrolled thermal conditions with consequences in terms of reliability or durability of the members and in terms of pollution for the environment.
In practice, it should be noted that the sharing of a degassing tank with several cooling loops is not without problems.
Indeed, the use of a single degassing tank for several cooling loops that are at different temperatures, 90/110° C. for a high temperature loop and 60° C. and 30° C. for low or very low temperature loops, has the direct consequence of disturbing the regulation of temperature that occurs in the low temperature regulation loops. In fact, the high temperature regulation loop will make a continuous supply of high temperature liquid in the lower temperatures loop(s).
Moreover, when operating at their respective nominal temperatures, the high temperature regulation loop has a constant need for degassing because the coolant which is in contact with hot spots of the engine—cylinder head cooling—can be vaporized punctually and therefore generate gas bubbles while the low or very low temperature regulation loops have a need for degassing at startup but do not generate gas bubbles during their operation. In other words, once the rise in temperature up to the nominal operating temperature is achieved, a degassing tank shared with a high temperature cooling loop and to one or more lower temperature cooling loop(s) turns out to have a deleterious effect on the cooling operation at lower temperature.
Degassing loop closing devices are already known for example from the document FR 2 949 509-A1 which are, however, inappropriate for the management of multiple cooling loops and their degassing problem.